On Tue, 17 Jul 2007, Rafael J. Wysocki wrote:
On Tuesday, 17 July 2007 14:48, Huang, Ying wrote:
On Tue, 2007-07-17 at 01:13 -0700, david@xxxxxxx wrote:
however, since the resume designed for ACPI won't work would the following
approach work
1. boot one kernel
2. setup a kexec the same way you would for hibernate
3. kexec to the new kernel
4. overwrite the memory of the first kernel
5. kexec 'back' to the main kernel that has now been overwritten by what was saved?
as part of this question, when you do a kexec, how does the kernel that
you are doing the kexec to know what to run next?
For kernel in 3 that do kexec, the devices and CPU state are saved into
memory before executing the new kernel. So when jumping back, the
control will continue from kexec point. If the memory image of main
kernel is restored from disk, the devices and CPU state in memory is
restored too. Before jumping back in 5, the devices are put in the known
state, after jumping back, the devices and CPU state is restored. If the
"kexec -j" is used to trigger the kexec in 3, the system will continue
with "kexec -j" exiting with exit code 0.
it needs to do some initialization first before it starts running normal
things, and at that point it the move back doesn't look for init like a
normal kernel boot (or the system would effectivly boot instead of picking
up where it left off)
I think the early initialization can be done in a initramfs. At that
point, the resume image can be checked, the next step depends on the
result of checking.
is this 'restart point' flexible enough that either the pre-hibernate
kerenl or the small hibernate kernel could tell the pre-hibernate kernel
to go into suspend-to-ram mode before doing anything else?
It is possible for hibernate kernel to pass information back to
pre-hibernate kernel. For example, the information can be passed in jump
buffer page.
I think it would be reasonable to have a protocol defined for passing this
information, so that it's independent of the kernel version etc.
At this point it looks like we have the following communication nessasary
between the two kernels
1. the original kernel needs to create a map of what memory to backup
this could be either a bitmap, or a series of address:blockcount pairs.
in either case the result could be sizeable, so it's probably best to
define a standard location to find the type and address of the data.
2. the new kernel needs to tell the old kernel which 'restart point' to
use.
this could be a simple jump table.
the list that has been suggested so far is
A. restore (the default)
B. suspend-to-ram
C. ACPI suspend-to-disk (S4 mode)
since both kernels have access to the other kernel's memory the data could
be stored in either kernel's address space, but my initial thought is that
it's cleaner to store this in the original kernel's space and have the
second kernel find it there.
I don't have the knowledge to create either of these interfaces, let alone
the pull to get them implmented in the kernel.
could I ask that one of you consider makeing a patch that implements at
least #1 (the memory map)
it sounds as if these kexec-back patches plus makeing the memory map
available would allow for a ACPI-free hibernate mode with no other
modifications. I'd like to try experimenting with this, but without the
memory map it sounds as if things will croak when I try to do this.
David Lang
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